A vertical cavity surface-emitting laser (VCSEL) device is a semiconductor laser device that emits light in a direction perpendicular to a substrate and has received attention due to its (1) competitive price, (2) low power consumption, (3) small size and high performance, and (4) ease of two-dimensional integration when compared with an end-surface-emitting semiconductor laser device that emits light in a direction parallel to the substrate.
The surface-emitting laser device has a constriction structure so as to improve a current inflow efficiency. As the constriction structure, a constriction structure (hereinafter also referred also to as an “oxidized constriction structure” for convenience sake) obtained by selectively oxidizing an Al (aluminum) As (arsenic) layer is generally used. The oxidized constriction structure is manufactured in the following manner. That is, a predetermined size of mesas having a selective oxidized layer made of p-AlAs exposed at their side surfaces are formed and then placed in a high-temperature steam atmosphere to selectively oxidize Al from the side surfaces of the mesas. With the oxidation of the Al, non-oxidized regions are formed in the selective oxidized layer near the centers of the mesas. The non-oxidized regions are regions (current injection regions) through which the driving current of the surface-emitting device passes. Thus, current constriction is easily made possible. The refractive index of the layer where Al is oxidized (AlxOy) in the oxidized constriction structure is about 1.6, which is smaller than that of a semiconductor layer. Accordingly, since a difference in the refractive index in a traverse direction occurs in a resonator structure and light is trapped at the centers of the mesas, a light-emitting efficiency can be improved. As a result, excellent characteristics such as a low threshold current and a high efficiency can be realized.
Meanwhile, since the surface-emitting laser device is susceptible to humidity (water), various countermeasures have been taken (see, for example, Patent Documents 1 through 3).
Furthermore, the surface-emitting laser device can suppress the rise in a junction temperature (active-layer temperature), reduce a gain drop, and obtain a high output by immediately discharging the heat generated in an active layer (see, for example, Patent Document 4).
With the countermeasures disclosed in Patent Documents 1 however, demanded reliability may not be obtained.